Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalgaPyropia haitanensis(Bangiales, Rhodophyta)

The present research investigated the effect ofpCO(2)levels (C), seawater temperature (T), and nutrient availability (N) on the growth and physiochemical changes inPyropia haitanensis. With nutrient enrichment, the interaction of higherpCO(2)increased relative growth rates (RGR) by 105.9% when temperature increased (22 degrees C) compared with the control (lower T, lower C, and lower N: LTLCLN). The higherpCO(2)decreased theP(m)rates at the lower temperature (18 degrees C), yet displayed no interaction with higher T or N levels. The higher N increased dark respiration rate (R-d) at 18 degrees C. At 22 degrees C, higherpCO(2)significantly enhanced the maximum ratio of (quantum yields (F-v/F-o) and the maximum quantum yield (psi(po)), while it sharply decreased the absorption of photons per active reaction center (ABS/RC) and dissipation of energy fluxes (per RC) (DIo/RC). Higher temperature obviously reduced theF(v)/F(o)and psi(po)under ambient CO(2)level. The higherpCO(2)significantly increased the phycoerythrin (PE) and phycocyanin (PC) contents, while higher temperature decreased the PE contents with elevated CO(2)and declined the PC content regardless of CO(2)condition. At lower nutrient condition, higherpCO(2)increased Chlacontent. Soluble carbohydrates (SC) and soluble protein (SP) content almost was unchanged among all treatments. Our findings indicate that nutrient availability may regulate photosynthetic mechanism to offset the negative effect of future ocean warming onP. haitanensis, thereby sustaining or increasing the biomass yield of the algae.